Once a fast cod, always a fast cod: maintenance of performance hierarchies despite changing food availability in cod (Gadus morhua).

To examine whether Atlantic cod maintain constant hierarchies of sprint speeds and muscle metabolic capacities under different feeding regimes, the physiological capacities of individual cod were followed through a starvation-feeding-starvation cycle. We examined sprint speeds and maximal enzyme activities in white-muscle biopsies at each period. We measured the glycolytic enzymes, phosphofructokinase (PFK) and lactate dehydrogenase (LDH), the mitochondrial enzyme, cytochrome C oxidase (CCO), and the biosynthetic enzyme, nucleotide diphosphate kinase (NDPK). Sprint speeds were measured in a laser diode/photocell-timed raceway. As expected, the feeding regime had a marked impact on the physiological capacities of cod, but the responses differed for sprint-swimming and muscle metabolic capacities. The different enzyme activities as well the condition index generally decreased during the first starvation, improved with feeding, and fell again during the second starvation. In contrast, sprint performance improved after feeding but did not fall with the second starvation. Although both the enzyme activities and the sprint speeds showed considerable interindividual variation, sprint speeds were not significantly correlated with the enzyme activities. The hierarchy of sprint performance of the cod was maintained, regardless of the preceding feeding regime, whereas those of muscle metabolic capacities were not.